The present invention relates to a screw compressor of the kind having two screw rotors journalled in meshing engagement in a housing which encloses a working chamber for each rotor and which incorporates a low pressure side-wall, a high pressure wall, an inlet port and an outlet port, and also an axial recess which includes a continuous part of the wall of both the rotor working chambers and extends out through at least the high pressure wall, there being mounted in said recess two slides which are arranged for mutually independent axial movement for controlling the built-in volume ratio and the capacity of the compressor.
Regulating slides of this and similar kinds play an essential part in effecting the changes in the volume ratio and the capacity of screw compressors which become necessary as a result of varying operating conditions. At the same time the regulating slides create a complication in an otherwise uncomplicated screw compressor.
Initially the two individual regulating slides were mounted in separate recesses in the rotor housing, as evidenced in Swedish Patent Specification No. 218 783 for example, particularly FIGS. 1 and 2 (corresponding to U.S. Pat. No. 3,088,659; FIGS. 5 and 6). Although this slide arrangement allows the slides to move axially individually of one another, without mutual interference in the event of slide-seizure due to thermal expansion, the provision of separately arranged slides creates difficulties and problems in manufacture and results in unavoidable throttling of the outlet port.
Consequently, attempts have been made to combine the two slides into a composite slide assembly similar to the conventional slide intended for regulating the built-in volume ratio, but with the one slide mounted for axial movement in the other slide, as disclosed in the publication "Annual DOE active solar heating and cooling contractors review meeting", September 81, U.S. Department of Energy. Although this slide design is constructionally more simple, it still throttles the outlet port to some extent. An additional drawback is that the bearing play in the outer slide is added to the bearing play in the inner slide. This additional play presents a serious disadvantage, since the inner slide carries the pointed spine part which projects inwardly to a location extremely close to the mesh point of the rotors and where contact therewith could have serious consequences. The risk of this happening is quite strong in view of the aforesaid combined play, and an object of the present invention is accordingly to provide a safer and improved design without incorporating further complications.